1. Field of the Invention
The present invention relates to a master carrier for magnetic transfer, which has a magnetic layer with a transfer pattern formed therein for transferring information data to a magnetic recording medium.
2. Description of the Related Art
Increasing the recording density of magnetic recording media is now in great progress so as to satisfy the requirement for the increase in information contents of today. In a magnetic recording medium having a high recording density, the information-recording region has a narrow track. In order to precisely trace a magnetic head along such a narrow track to thereby reproduce signals at a high S/N ratio, a tracking servo technique for magnetic heads is an important theme.
In order that a magnetic head could trace along the recording track of a magnetic recording medium, the recording medium must be preformatted with the necessary servo information that includes positioning servo signals, tracking address signals and regeneration clock signals, while it is produced.
For preformatting magnetic recording media, a dedicated servo-write device (servo track writer) is used at present. With it, however, a magnetic head must be scanned on every magnetic recording medium for preformatting it one by one, and it takes a long period of time. Therefore, for increasing the productivity in preformatting, a large number of servo-write devices must be driven all at a time. However, introduction and maintenance of such a large number of servo-write devices is expensive.
It is anticipated that increasing the recording density of magnetic recording media will be in greater progress in future and the track density thereof will therefore further increase.
In that situation, a study of magnetic transfer is now in progress, which comprises keeping the surface of a magnetic recording medium that has a magnetic recording region in its surface, in intimate contact with the surface of a master carrier that has a transfer pattern of servo signals and others formed of a magnetic material on the surface of a support thereof, and applying a transfer magnetic field to the master carrier in that condition to thereby magnetically transfer the transfer pattern of the master carrier to the magnetic recoding medium all at a time.
When the magnetic recording media referred to hereinabove are disc-shaped ones such as hard discs or high-density flexible discs, then a disc-shaped master carrier is kept in intimate contact with one or both faces of the magnetic recording medium of the type and, in that condition, a transfer magnetic field is applied to one or both surfaces thereof by the use of a magnetic field applicator with electromagnets or permanent magnets (for example, see U.S. Pat. No. 6,347,016).
For correctly transferring and recording a transfer pattern of a master carrier to a magnetic recording medium (slave medium) in a mode of magnetic transfer, it is important to apply a magnetic field to the magnetic recording medium while it is in uniform and intimate contact with the master carrier.
FIG. 8 is an explanatory view schematically showing a conventional master carrier 100 and a magnetic recording medium 200 that are put on top of each other. As in FIG. 8, when there exists a space S between the master carrier 100 and the magnetic recording medium 200, then the fine uneven transfer pattern (not shown) provided in the transfer region of the master carrier 100 could not be in uniform and intimate contact with the magnetic recording region formed in the surface of the magnetic recording medium 200 and therefore the transfer pattern could not be correctly transferred to the magnetic recording region.
The cause of the space S would be that the warp or distortion occurred in the master carrier 100 may be high-ordered when kept in intimate contact, and the support 101 of the master carrier 100 is thereby deformed, and the face of the support 101 is curved.
FIG. 9 is a plan view of the master carrier 100 of FIG. 8, seen on its top. FIG. 10 is a graphical view showing the warp of the master carrier 100 of FIG. 9, in the radial direction thereof (in the direction of the arrow R in the drawing). FIG. 11 is a graphical view showing the distortion of the master carrier 100 of FIG. 9, in the peripheral direction thereof (in the direction of the arrow C in the drawing).
“Warp” as referred to herein means the displacement of the support surface in the radial direction of the master carrier, as in FIG. 9 and FIG. 10. “Distortion” also referred to herein means the displacement of the support surface in the circumferential direction of the master carrier, as in FIG. 9 and FIG. 11.
Heretofore, a magnetic field is applied to a magnetic recording medium and a master carrier that are in uniform and intimate contact with each other while an external load is applied there to so as not to form a clearance gap between the two. However, since the master carrier is warped or distorted by itself, it is extremely difficult to ensure uniform and intimate contact between the mater carrier and the magnetic recording medium attached thereto.
On the other hand, it was impossible to completely remove warp and distortion from master carriers in view of the process of producing them.
For these reasons, there occurs a space between the magnetic recording medium and the master carrier that are kept in contact with each other, owing to the high-ordered warp and distortion of the master carrier, and, as a result, the transfer efficiency is lowered and magnetic recording media could not be correctly preformatted. In this point, there is still room for improvement in the transfer technique.